Silver halide photographic material containing antifog agent with protected mercapto group

ABSTRACT

The invention relates to silver halide photographic material containing an antifog agent having the formula   WHEREIN A is a nitrogen-containing heterocyclic radical or a 4acetaminophenyl radical, R is H, alkyl of 1 to 4 carbon atoms, aryl or   AND N IS 2 TO 4.

Unite States atent [1 1 Abele et al.

[ June 10, 1975 Rudolf Schneider, Sprendlingen, both of Germany E. I. du Pont de Nemours & Company, Wilmington, Del.

Filed: Oct. 12, 1973 Appl. No.: 405,801

Assignee:

Foreign Application Priority Data Oct. 13, 1972 Germany 2250136 us. Cl. 96/76 R; 96/109 rm. Cl G036 1/34 Field of Search 96/109; 96/76 R References Cited UNITED STATES PATENTS 12/1954 Knott 96/109 6/1960 Dersch et a1 96/109 8/1960 Angelus et a1. 96/109 2,981,624 4/1961 Dersch et a1 96/109 Primary Examiner-Won H. Louie, Jr.

[57] ABSTRACT The invention relates to silver halide photographic material containing an antifog agent having the formula wherein A is a nitrogen-containing heterocyclic radical or a 4-acetaminophenyl radical,

R is H, alkyl of l to 4 carbon atoms, aryl or CO CH-S -A and n is 2 to 4.

7 Claims, No Drawings SILVER HALIDE PHOTOGRAPIIIC MATERIAL CONTAINING ANTIFOG AGENT WITH PROTECTED MERCAPTO GROUP This invention relates to photographic material having a light-sensitive silver halide emulsion which is stabilized against over-development fog.

If photographic materials are processed under intensified conditions, for example, with highly active developer solutions, by development at relatively high temperatures or extremely transient utilization of the development, there exists a danger that silver halide grains which do not carry any latent image nuclei will also be reduced. The fog produced by this undesired reduction of unexposed silver halide grains, under the above-mentioned conditions, appears particularly strongly toward the end of the normal development process and is also called overdevelopment fog. This overdevelopment fog cannot be prevented by the conventional stabilizing agents or can be prevented only by sacrificing optimum sensitivity.

Thus, for example, the stabilizers from the class of triazaindolizines, which are outstandingly suitable for the prevention of storage fog, do not provide suitable protection against overdevelopment fog, because their protective action abates and practically disappears through diffusion displacement and other mechanisms toward the end of the development exactly when they are most needed. Other stabilizers of known effectiveness, such as mercury compounds or heterocyclic mercapto compounds are indeed capable of reducing the development fog in the normal and also in the overdevelopment region, but have the big disadvantage that when used in sufficient quantities they reduce considerably the sensitivity of the photographic emulsions.

A fundamental disadvantage of the direct addition of the heterocyclic mercapto compounds, which in themselves are particularly active against overdevelopment fog, to silver halide emulsions consists in that they are completely active from the time of their addition, that is, also during the casting process, during the total time of storage of the unprocessed film material and finally already in the initial stage of the photographic development. Therefore, one is forced to accept desensitization effects even before processing, and incomplete utilization of the sensitivity of the material during the development itself. To solve this problem, attempts have already been made to substitute the mercapto group of these compounds by suitable hydrolyzable radicals and therewith inactivate them for the period in which they are not supposed to act but, on the other hand, to permit them to be liberated again in active form during the development process through hydrolysis. Such substituents are usually thioesters or thioethers of the mercapto stabilizer.

Substituents of the thioester type, for example carboxylic acid or sulfonic acid groups, or groupings of carbonic acid derivatives, for example carbalkoxyl groups, are known from many Patents: for example, from German Pat. No. 1,597,503, U.S. Pat. No. 3,260,597 and German Offenlegungsschrift No. 2,061,972. They all have the disadvantage that they do indeed cleave more or less rapidly in the alkaline medium of the developer, but hydrolytic cleavage takes place, even though slowly, already in neutral or weakly acid pH regions. This has the consequence that one can indeed add these protected stabilizers in inactive form to the emulsion, but if the period up to the casting of the emulsion and its drying is sufficiently long, an undesired densensitization of the emulsion is produced by a partial hydrolysis.

In contrast hereto, substituents of the thioether type, for example, those of U.S. Pat. Nos. 2,981,624 and 3,260,597, German Pat. No. 1,173,796 and German Offenlegungsschrift No. 1,908,217, are indeed stable in neutral or weakly acid media, but do not react during the development process, or react much too slowly or only at higher concentrations and, therefore, cannot prevent overdevelopment fog, at least not in the desired degree.

Therefore, an object of the present invention consists in providing antifog agents with inactivated mercapto groups which are completely stable in the neutral or weakly acid pH region of the emulsion but, on the other hand, in the alkaline pH region liberate the active stabilizer to the desired extent during development.

It has now been found that certain thioethers satisfy these conditions optimally. They correspond to the general formula:

1 Ell-C0 and n is 2 to 4.

Suitable compounds of this type are listed in Table 1 under the numbers l-9, of which the compounds 2, 5, 6 and 9 are preferred in the present invention.

Other heterocyclic radicals A contemplated are, for example, the thiodiazolyl, thiazolyl, oxazolyl, imidazolyl, benzimidazolyl, pyrimidinyl and triazolyl radicals. The heterocyclic radical A is the heterocyclic radical of a mercapto antifog agent and is usually substituted as illustrated in the compounds of Table 1. Compounds derivable from l-phenyl-5-mercaptotetrazole are particularly preferred. In such compounds, A is a lphenyltetrazolyl radical as shown in Compounds 1-4 and 8 of the compounds of the invention. It is preferred that the heterocyclic radical A have 5 or 6 atoms in the heterocyclic ring.

Table 1.

Compounds of the Invention Com ound 1 Melting point 120 0 Compound 2 Melting point 138 C 92529325.; Melting point 182 C i mmszii Melting point 177 C m- CH -CH -Nb swung, N N" 0 0 I Compg nd 5 Melting point 122 C Melting point 179 0 131g 16 l Continued Compougil Melting point 150 C Melting point 186 0 miuu Melting point 163 c Compounds -01" the Prior Art Q91P&L l

L H German patent 1, 173,336

Compounc l l] @T--IEI-CO-O-CH CH O 3 German Offenlegungs- K Y schrift 2,061, 972

Comgound l2 N--C-S -CH -C U 5, atent 2,981,624

Production of the new compounds is accomplished simply from the mercapto group-containing antifog agent and an N-substituted derivative of maleimide by boiling equivalent quantities in alcoholic solution.

To produce the light-sensitive materials, the antifog agents are added to the light-sensitive emulsions or also to the light-insensitive auxiliary layers, such as interlayers, protective layers and the like. The addition takes place most favorably before casting the emulsion, but it is also possible to add the compounds at another point in the production of the emulsion. When used in the emulsion layer itself, the compounds preferably are added in quantities of 0.05 to mmol based on 1.0 mols of silver halide added, whereas in the auxiliary layers they display the best effect in quantities of 0.1 to 5 mmols.

In every case, the optimum quantity naturally depends on the nature of the antifog agent and the emulsion used and can be determined easily from case to case.

The compounds described can be dissolved in a suitable solvent and added to the emulsion in this form. If the solubility of the compounds in water-miscible organic solvents is too small, they can also be dissolved in a known manner in water-immiscible organic solvents and added in the form of a dispersion. Examples of suitable solvents are 4-phenyl-1,3-dioxane, tributyl phosphate, diethyl phthalate, ethyl acetate, phenyl glycol and the like.

The new antifog agents can be used in the most varied kinds of reproduction materials, for example, in nonoptically sensitized materials, such as X-ray films, but just as well also in orthochromatically and panchromatically sensitized reproducing materials. Moreover, the light-sensitive emulsions used may contain the customary additives, such as chemical sensitizers, hardeners, wetting agents, and the like. Furthermore, the new antifog agents can be used in mixtures with one another or in combination with other antifog agents.

EXAMPLE 1 EXAMPLE 2 This example describes the preparation of Compound 6 of Table 1. 4-Mercaptoacetanilide (1.67g 0.01 mol) is heated to boiling under reflux for 3 hours with 1.25 g (0.01 mol) of N-ethylmaleimide in 50 ml of ethanol. Subsequently the mixture is evaporated to dryness in a vacuum and the residue is recrystallized from 1:1 ehtanol/benzene. Yield: Practically quantitative Mp 179 C.

The preparation of the other compounds of the invention takes place in an analogous manner.

EXAMPLE 3 To determine the stability of various S-substituted 1-phenyl-5-mercaptotetrazoles in different pH regions,

the quantity of free mercapto stabilizer split off after a, definite time of standing was determined.

For this, in every case 1 mol of the compounds 2, l0, 1 1 and 12 in Table 1 was dissolved in -5ml of 4-phenyl- 1,3-dioxane and emulsified in ml of 3% gelatin with a high-speed stirrer for 5 minutes with the addition of 1 ml of a 10% aqueous solution of the sodium salt of Table 2 pH Compounds according to the art Compound no.

2 of Table 1 No. 10 in No. 11 in No. 12 in according to Table 1 Table 1 Table l the inven- (thioester) (thioester) (thioether) tion EXAMPLE 4 An optically unsensitized, high sensitivity silver halide emulsion with about 10 weight percent of gelatin and about 10 weight percent of silver halide was prepared as an experimental emulsion, in which the silver halide consisted of 98 weight percent of silver bromide and 2 weight percent of silver iodide.

The emulsion is divided into five portions A, B, C, D and E. Portion A contains no additive and serves as a comparison sample. The quantities of additives, dissolved in acetone, presented in Table 3 were added to portions B, C, D and E per mol of silver bromide. Subsequently the portions A to D were halved (part I and part 11) and cast on a polyester film base immediately or after 1 hour/35 C. The light-sensitive material was evaluated in the customary manner.

For this, the samples, in the form of the known test strips, were exposed for 2 sec with two Osram lamps (Wi 9 2,660 K) at a distance of 1.2 m in a gray wedge sensitometer with a wedge constant of D ='0.15/cm with filters BG 3 (1.8 .mm) and BG 38 (1.5mm), and then developed at 35 C for 25 sec and 50 sec with a developer having the following composition:

Hydroquinone 30.00g l-Phenyl-3-pyrazolidone 1.00g Na SO (anhydrous) 60.00g KOH 23.00g NaB0 -4H O 20.00g water to make up to 1 l.

The products were then fixed in a customary fixing bath, subsequently Washed and dried.

In the following results, the value for the general sensitivity of the comparison emulsion is set equal to 100:

Table 3 No time of standing 25 sec 35C 50 sec 35C Fog Relative Fog Relative Part I sensisensitivity tivity A Control without 0.07 l 0.36 l4l stabilizer B 0.3 mmol of com- 0.06 98 0.2l 138 pound 2 Table l C 0.1 mmol of com- 0.05 91 0.20 132 pound 10 Table l D 0.2 mmol of com- 0.05 l00 0.l 145 pound ll Table l E 1.0 mmol of com- 0.07 l00 0.34 148 pound 12 Table l Emulsion standing time 25 sec 35C 50 sec 35C I hour at 35C Fog Relative Fog Relative sensisensi- Part ll tivity tivity A Control without 0.07 100 0.40 148 stabilizer B 0.3 mmol of com- 0.06 98 0.28 l4l pound 2 Table l C 0.2 mmol of com- 0.05 85 0.25 l20 pound Table l D 0.3 mmol of com 0.05 87 0.20 125 pound ll Table l E 1.0 mmol of com- 007 100 0.38 151 pound l2 Table I It is seen that the thioester stabilizers according to the state of the art, which are cleavable by alkali but are not stable in the emulsion (Compounds 10 and l 1 of Table l as expected, indeed act against the overdevelopment fog, but on standing of the emulsion at 35 C even after 1 hour they cause considerable losses in sensitivity. The thioether (compound 12 of Table 1) according to the state of the art, which does not cleave sufficiently fast, even at a high concentration, indeed gives no loss in sensitivity, but also no improvement of the overdevelopment fog.

On the contrary, the compound 2 of Table l in Part II of the Example 4 displays a very good improvement of the overdevelopment fog and only an extremely small lowering of the sensitivity.

In the Examples 5 to 8 are presented additional representations of the antifog agents of the invention showing their activity compared to the unprotected fundamental stabilizer.

EXAMPLE 5 A silver halide emulsion prepared according to the information of Example 4 is divided into seven parts A, B, C, D, E, F and G, in doing which part A serves as a comparison sample. To each of the remaining parts one of the additives in Table 4 in acetone solution was added and after a standing time of 1 hour at 35 C was cast on a polyester film base. The further processing followed that in Example 4.

10 Table 4 Emulsion standing time 25 sec 35C 50 sec 35C I hour at 35C Fog Relative Fog Relative sensisensitivity tivity Part A Control without 0.07 100 0.40 138 stabilizer B 0.] mmol of l- 0.04 85 0.26 l 12 phenyl-S-mercaptotetrazole C 0.2 mmol of com- 0.06 l02 0.25 l35 pound 8 Table l D 0.2 mmol of com- 0.05 98 0.24 I38 pound I Table l E 0.3 mmol of com- 0.06 98 0.28 l4l pound 2 Table l F+ 0.3 mmol of com- 0.06 l02 0.29 145 pound 3 Table l G 0.2 mmol of com- 0.06 96 0.23 132 pound 4 Table 1 EXAMPLE 6 An optically unsensitized, high sensitivity silver halide emulsion with about 5 weight percent of gelatin and about 10 weight percent of silver halide is produced. The silver halide consists of 98 weight percent of silver bromide and 2 weight percent of silver iodide. The emulsion produced in this way is divided into three parts A, B and C. Part A contains no additive and serves as a comparison sample. Parts B and C contain the quantities of additives given in Table 5 per mol of silver bromide. After a standing time of 1 hour at 35 C the emulsions are cast on a polyester film base and processed further as in Example 4.

A silver halide emulsion prepared like that in Example 6 is divided into four parts A, B, C and D, whereby part A serves as a comparison sample. To each of the remaining parts B, C and D is added per mol of silver bromide one of the additives presented in Table 6 in acetone solution and, after a standing time of one hour at A silver halide emulsion prepared according to the information in Example 4 is divided into three parts A, B and C. Part A contains no additive and serves as a comparison sample. Parts B and C contain the quantities of additives per mol given in Table 7. After a standing time of 1 hour at 35 C, the emulsions are cast on a polyester film base and processed further as in Example 4.

Table 7 Emulsion standing time 25 sec 35C 50 sec 35C I hour at 35C Fog Relative Fog Relative sensisensitivity tivity Part A Control without 0.12 100 0.43 141 stabilizer B 0.1 mmol of free 0.09 83 0.30 l06 Z-mercaptobenzoxazole C 0.4 mmol of com 0.ll 102 0.28 138 pound 9 Table 1 It is evident in all cases that each of the protected sta- 4O 4 photographic material according to claim bilizers; even with standing of the emulsion, exerts a good antifog effect but, on the othher hand, compared with the strongly desensitizing free fundamental stabilizer displays no or only a relatively small loss in sensitivity.

Compared with the known state of the art, the new stabilizers are characterized chiefly in that, at pH values of l and above, they are very easily cleavable, whereas they are absolutely stable at the same time in the pH region between 3 and 7. As a result of this, there is the great advantage that these compounds, even when they are in contact with the light-sensitive emulsion for a long time before the casting, which is always the case under production conditions, are stable and display no tendency toward hydrolysis in this pH region, so that even with very long standing time, there is no desensitization.

What is claimed is:

l. Photographic material comprising a film support and at least one light-sensitive silver halide emulsion layer containing an antifog agent or being in contact with an auxiliary layer containing an antifog agent, said antifog agent being present in an antifogging amount and having the formula:

ca -co ,CO-CH-S-A on N n co-CH and n is 2 to 4.

2. Photographic material according to claim wherein R represents an ethyl radical.

3. Photographic material according to claim wherein A represents a benzothiazolyl radical.

wherein A represents a 4-acetaminophenyl radical. 5. Photographic material according to claim wherein A represents a benzoxazolyl radical.

6. Photographic material according to claim, wherein A represents a l-phenyltetrazolyl radical.

7. Photographic material according to claim wherein A is selected from l-phenyltetrazolyl, benzothiazolyl, 4-acetaminophenyl, and benzoxazolyl radicals. 

1. PHOTOGRAPHIC MATERIAL COMPRISING A FILM SUPPORT AND AT LEAST ONE LIGHT-SENSITIVE SILIVER HALIDE EMULSION LAYER CONTAINING CONTAINING AN ANTIFOG AGENT, SAID ANTIFOG AGENT BEING PRESENT AN ANTIFOG AGENT OR BEING IN CONTACT WITH AN AUXILLYR LAYER IN AN ANTIFOGGING AMMOUNT AND HAVING THE FORMULA:
 2. Photographic material according to claim 1, wherein R represents an ethyl radical.
 3. Photographic material according to claim 1, wherein A represents a benzothiazolyl radical.
 4. Photographic material according to claim 1, wherein A represents a 4-acetaminophenyl radical.
 5. Photographic material according to claim 1, wherein A represents a benzoxazolyl radical.
 6. Photographic material according to claim 1, wherein A represents a 1-phenyltetrazolyl radical.
 7. Photographic material according to claim 2, wherein A is selected from 1-phenyltetrazolyl, benzothiazolyl, 4-acetaminophenyl, and benzoxazolyl radicals. This example describes the preparation of Compound 5 of Table
 1. 2-Mercaptobenzothiazole (1.67g 0.01 mol) is heated to boiling under reflux for 3 hours with 1.25 g (0.01 mol) of N-ethylmaleimide in 50 ml of ethanol. Subsequently the mixture is evaporated to dryness in a vacuum and the residue is recrystallized from methanol. Yield: Practically quantitative Mp 122* C. EXAMPLE 2 This example describes the preparation of Compound 6 of Table
 1. 4-Mercaptoacetanilide (1.67g 0.01 mol) is heated to boiling under reflux for 3 hours with 1.25 g (0.01 mol) of N-ethylmaleimide in 50 ml of ethanol. Subsequently the mixture is evaporated to dryness in a vacuum and the residue is recrystallized from 1:1 ethanol/benzene. Yield: Practically quantitative Mp 179* C. The preparation of the other compounds of the invention takes place in an analogous manner. 